1. Field of the Invention
The present invention relates to a backlight module used in a liquid crystal display, and more particularly, to a backlight module with a brightness enhancement film having a plurality of spherical surface microlenses.
2. Description of the Related Art
A backlight module is a key component of a liquid crystal display (LCD). The purpose of the backlight module is to provide a sufficient-brightness and an even-distribution light surface to the LCD panel. Because the LCD is widely used in various electronic products such as a monitor, a notebook computer, a digital camera, and a projector, the demand for the backlight module has increased tremendously.
Please refer to FIG. 1, which shows a prior art of a backlight module 20. The backlight module 20 comprises a light source 22 (such as a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a light emitting diode), a light guide plate 26, a reflector 24 disposed at a side of the light guide plate 26, a diffusion sheet 28, and prism sheets 30 and 32. The reflector 24 is used for reflecting light from the light source 22 toward the light guide plate 26. Then the light guide plate 26 guides light emitted from the light source 22 and light reflected from the reflector 24 as uniform planar light. Through the light-distributing of the diffusion sheet 28 and light-gathering of the prism sheets 30 and 32, the light is fed into an LCD panel. The prism sheets 30 and 32 are formed by hardening an acrylic resin on a polyester film with a thickness of 125-μm by means of exposure under high energy UV light. The conventional prism sheets 30 and 32 are served as bar-alignment triangle prisms in characteristics of a vertex angle of substantial 90 degrees with an interval of 50 μm within each other. The prism sheets 30 and 32 can concentrate scatter light from the light guide plate 26 upward with substantial ±35 degrees with respect to a direction of an on-axis. Nevertheless, as shown in FIG. 1, the prism sheet 30 only concentrate light constituent of Y-axis upward, and the prism sheet 32 only concentrate light constituent of X-axis upward. Therefore, utilizing only a single prism sheet can enhance the brightness by 1.6 times, while, for better light-gathering quality, utilizing two prism sheets 30 and 32 with their prism alignments thereon being vertical to each other can enhance the brightness by 2 times or more. In other words, scatter light is gathered by means of prisms on the prism sheets 30 and 32, therefore boosting the brightness of the LCD display by 2 times. In this manner, for the LCD display described above, power consumption is lowered and a life span of batteries is lengthened.
Consequently, using a single prism sheet fails to provide sufficient brightness, while using two prism sheets may result in more photo-energy consumption. Besides, using two prism sheets may induce higher cost for the backlight module as a result.